Further, the camera does not detect the power save state of the printer, and the implementation becomes easy. Even when the PS state of the printer changes, no detection timing difference is generated, and no loss of a packet transmitted by the camera occurs.
(Third Embodiment)
A network configuration in the third embodiment is the same as that in the first embodiment, and is shown in FIG. 1. In FIG. 1, reference numeral 101 denotes a camera; and 102, a printer. The internal configurations of the camera 101 and printer 102 are the same as those in FIGS. 2 and 3, and a description thereof will be omitted.
In the third embodiment, the camera 101 does not manage the power save state of a partner, and transmits data in accordance with the sequence of FIG. 6. When the power save state of the camera 101 changes, the camera 101 transmits an ATIM and dummy data to explicitly notify the partner of the power save state. The printer 102 manages the power save state of a partner, and transmits data in accordance with the sequence of FIG. 12.
When the camera 101 explicitly transmits its power save state, it explicitly notifies the partner of the power save state of the camera 101 by transmitting an ATIM packet and dummy data packet regardless of the power save state of the partner. The flow of PS state notification by the camera 101 will be explained with reference to FIG. 8. The description of the flow assumes that the camera 101 and printer 102 have already configured an adhoc network.
A host CPU 201 of the camera generates a power save state change request such as an EnterPS command or ExitPS command to a wireless unit 205 (S801). The EnterPS command will be exemplified. Upon reception of the PS state change request, the wireless unit 205 determines whether the camera is in the ATIM Window (S802). The flow waits for the ATIM Window timing, and then an ATIM packet having PS=1 in the MAC header is transmitted by a broadcast receivable by all terminals in the adhoc network (S803). By the broadcast, all terminals (in this case, only the printer 102) in the adhoc network keep the Awake state till the next beacon reception. In the broadcast, no ACK reception is done. After ATIM transmission, the flow waits for the end of the ATIM Window period (S804). Then, the PS in the MAC header is changed to “1”, and a null data packet containing no data in the data field is broadcasted (S805). Since all terminals (in this case, only the printer 102) in the adhoc network keep Awake, they receive the null data.
After null data is transmitted, the wireless unit 205 of the camera changes the PS state of the camera (S806), and starts intermittent reception.
In the above description, null data can also be omitted to transmit only an ATIM packet before a change in state. When only a specific terminal in a network is notified of a change in state, not a broadcast packet but an ATIM packet and null data may be transmitted to a specific MAC address. Further, in an ATIM Window in which a terminal transmits a beacon, the terminal may notify other terminals of a change in PS state by only a beacon without transmitting any ATIM or null packet.
FIG. 9 shows a case wherein STA 1 notifies STA 2 of a PS change by only an ATIM packet. Assume that a PS state change request is generated in ATIM Window 2. The camera 101 transmits an ATIM packet in ATIM Window 2 before changing to PS=on, and the PS state is changed to PS=on in the next beacon interval 3 subsequent to the interval in which the packet has been transmitted. STA 1 keeps Awake in beacon interval 3 in order to transmit a beacon, and can shift to the Doze level in beacon interval 4 (not shown).
As described above, an ATIM and null data are transmitted before the power save state is changed, and then the PS state is changed. With this operation, terminals in an adhoc network can be reliably notified of a change in state without detecting the PS state of a partner. Also, a time lag between the PS state notifying side and the PS state detecting side can be prevented, thus preventing generation of any packet loss.
As has been described above, according to the above embodiments, the load of detecting and managing the power save state of a partner on a transmitting station can be reduced, and the implementation becomes easy. Since no difference in update timing is generated between the power save state notifying side and the power save state detecting side, and a packet loss (data reception error) by an update timing difference can be reduced. Compatibility with a conventional terminal can be ensured, and connectivity can be improved by explicitly transmitting an ATIM, null data, and the like.
As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.
Claim Of Priority
This application claims priority from Japanese Patent Application No. 2004-273133 filed on Sep. 21, 2004, the entire contents of which are hereby incorporated by reference herein.